The use of constructions comprising a body formed from ultra-hard materials such as diamond, polycrystalline diamond (PCD), cubic boron nitride (cBN), polycrystalline cubic boron nitride (PcBN) are well known in the art. An example of such can be found in the form of cutting elements comprising an ultra-hard component or body that is joined to a metallic component. In such cutting element embodiment, the wear or cutting portion is formed from the ultra-hard component and the metallic portion is provided for the purpose of attaching the cutting element to a desired wear and/or cutting device. In such known constructions, the ultra-hard component can be formed from those ultra-hard materials described above that provide a high level of wear and/or abrasion resistance that is greater than that of the metallic component.
The use of PCD as an ultra-hard material for forming such constructions is well known in the art. PCD is formed by subjecting a volume of diamond grains to high pressure/high temperature (HPHT) conditions in the presence of a suitable catalyst material, such as a solvent catalyst metal selected from Group VIII of the Periodic table. Such PCD material is typically used to form the ultra-hard body that is attached to the metallic substrate. An issue that is known to exist with such conventional diamond bonded constructions comprising an ultra-hard body formed exclusively from PCD is that it is subject to thermal stresses and thermal degradation at elevated operating temperatures, due to the presence of the solvent metal catalyst, which is known to limit the effective service life of the construction when subjected to such operating temperatures.
Attempts to address such unwanted thermal performance of conventional PCD constructions have included removing the catalyst material, or solvent metal catalyst material, either partially or completely therefrom. For example, one known approach has involved removing the catalyst material completely from the PCD construction after it has been sintered, e.g., by the HPHT process noted above, by subjecting the PCD construction to a leaching process for a period of time that has resulted in the formation of a diamond bonded body that was substantially free of the catalyst material. The diamond bonded body resulting from such leaching process is referred to in the art as being thermally stable polycrystalline diamond (TSP) because the catalyst material has been removed therefrom.
While conventional TSP does have improved properties of thermal stability, abrasion and wear resistance at elevated temperatures when compared to conventional PCD, it lacks desired properties of strength, toughness, impact resistance and room-temperature hardness that were provided by the presence of the catalyst solvent metal. Thus, such conventional TSP while being well suited for some high temperature operating conditions, is not well suited for all such applications, e.g., those calling for properties of impact resistance, strength and/or toughness. Further, conventional TSP does not lend itself to attachment with a metallic substrate by HPHT process, and either has to be attached to a metallic substrate or directly to the end use application device by braze process. The need to attach the TSP body in this manner to a metallic substrate or to the end use device presents a further failure mechanism during operation due to the different material properties of the TSP body and substrate, and the related inability to form a strong attachment joint therebetween, which shortcomings operate to reduce the effective service life of cutting elements formed therefrom.
Another known approach aimed at improving the thermal stability of conventional PCD constructions involves removing the catalyst material from only a selected region of the PCD body, and not from the entire PCD body. Such removal of the catalyst material from only a region of the PCD body is achieved by subjecting the targeted region of the PCD body to a leaching agent for a period of time to provide a desired depth of catalyst material removal, and thereby leaving the catalyst material in a remaining region of the PCD body. This approach results in improving the thermal stability of the PCD construction at the treated region, while allowing the metallic substrate to remain attached to the construction. While this approach did improve the thermal stability of the PCD construction, and did provide a PCD construction having a strong substrate attachment, it is believed that further improvements in optimizing the desired performance properties of thermal stability, abrasion and wear resistance, strength, impact resistance, and toughness can be achieved.
It is, therefore, desired that a diamond bonded construction be provided in a manner that provides a desired optimized combination of thermal stability, wear and abrasion resistance, strength, impact resistance, and toughness when compared to conventional PCD, conventional TSP, or to the past attempts described above. It is further desired that such diamond bonded construction be produced in a manner that is efficient and does not involve the use of exotic materials and/or techniques.